how to - basic understanding of auto torque and horsepower - torque versus horsepower

[177SCmaro]

There is no such thing as "free energy". Turbos might generally be more efficient at creating boost than a roots supercharger, but they still take horsepower from the engine to operate.

The energy required to force all that extra air into the engine has to come from somewhere.

[MoronAntidote]

@177SCmaro

True, and the real effect of turbos is to effectively increase the engine's capacity as a function of boost. An engine which ingests more air via boost needs more fuel accordingly, but since it usually has lower compression and hotter intake temperature, the effective capacity increase does not scale with the boost. It's a good way to increase the output of a smaller, lighter engine, but it's not free power by any means, and it does add complexity. Great for diesels!

[177SCmaro]

@MoronAntidote Great for a 383 Chevy too.

[MoronAntidote]

@177SCmaro

Great for any engine up to a point. But let's not pretend they'll last as long as intended ;)

[177SCmaro]

@MoronAntidote You build them right and they last as long as intended. Besides, a engine isn't running boost all the time. For example, my supercharged 383 spends 99% of its time cruising around as a 8.75 to 1 low stress motor. With low boost it makes around 500HP. Compare that to runing around town with a high compression/rpm NA 383 with the same HP and I promise you my SC 383 would live longer. (And is a hell of a lot more streetable too!)

[MoronAntidote]

@177SCmaro

I appreciate your enthusiasm, but what we're talking about is increased peak power vs average power over time. Yes, you could achieve the same longevity as a stock engine if you were careful, but people who build engines in this way do so because they enjoy the thrill of acceleration. I'll accept it's well built and tuned, but i'll wager my left leg you boot it enough to 'on average' stress the engine greater than a stock engine could be stressed. I would, so why argue?

[MoronAntidote]

@177SCmaro

Btw i had no intention of getting into this kind of argument. I drive a stock e46 330i and i appreciate it. I have no desire to get caught up in arguments about particular engines, but as an engineer, i get frustrated by all the bullshit about torque vs horsepower. That's the only reason i posted tbh.

[ramentasty8]

so is horsepower dependent on rpm? or the ratio with rpm and torque?

[chughes374]

@ramentasty8 I dunno, ask 'davidsfarmlives' and link to this video

[jvanegas14]

@ramentasty8 torque times (rpm/5252)= horsepower, for a conventional engine.

[Seattlecarnut]

That's what I like about diesel engines, they produce most of their torque at low rpms. Like, for example, a 1.8 litre turbodiesel engine puts 120 bhp @ 3500 rpm and, say 200+ ft-lbs. of torque @ 1800 rpm.

[MoronAntidote]

@Seattlecarnut

Makes for a very transient unexciting experience. A brief squirt then all over.

The torque sounds good on paper, but because the rpm range is so low, the gearing is stretched, so you have no more torque at the wheels. It's wheel torque that determines acceleration.

[Seattlecarnut]

@MoronAntidote In that case, the more torque, the faster the acceleration.

[MoronAntidote]

@Seattlecarnut

Wheel torque determines acceleration, not engine torque.

Low revving engines requires taller gearing, which reduces wheel torque.

If you made that engine produce its torque over a wider rpm range, you could use shorter gearing, and produce more wheel torque.

[MoronAntidote]

@Seattlecarnut

Power to weight ratio is the best indicator of acceleration, given appropriate gearing.

Torque means nothing by itself. Power at a given rpm is the size of the pie. The gearing determines how you divide up the pie. You basically trade torque (acceleration) for speed in that gear. Either way, the bigger the pie the better, so power wins.

[MoronAntidote]

@Seattlecarnut

You do realise that gearboxes and final drives modify the engine torque don't you?

I suspect not, and this is one of the main reasons why people can't grasp the torque/horsepower thing. This video doesn't help at all, because it's trying to explain something in words which is best explained mathematically. Once you see the math it all becomes clear. I don't think you get it right now.

[ichigokillsyou]

Hi, so why does a car with more torque accelerate faster at lower rpm? also why wont having a lot of torque make a car fast alone? why is hp needed also?

[dualCranKy]

@ichigokillsyou The power itself is just the HP.

A car with more torque usually creates that torque in lower RPM, so it will have indeed also more HP, which is the important thing, in the lower RPM.

[ichigokillsyou]

@dualCranKy so what does torque specifically do for a car, say other than used for pulling stuff like in a truck. why is torque important in drifting also?

[dualCranKy]

@ichigokillsyou Its not really important... What is important is, that you choose the right gearbox for the right speeds...

Example:

You could get out of 50 Nm like 500 Nm with the right gear.

But instead of 1000 RPM your car would only transfer 100 to the tires.

But if your car can spin up to 10000RPM you could transer 1000 RPM to the tires.

I wasnt really right with my first post...

I depends on when the car creates how much torque and usually the better the powerband, the higher the hp.

[MoronAntidote]

@dualCranKy

NO NO NO

Acceleration at any rpm is proportional to engine torque, gearing, weight, drag and losses. HP is proportional to engine torque and rpm, and apart from transmission loss is conserved at the wheels regardless of gearing etc. Since engine horsepower is the product of torque and rpm, then the higher the horsepower, the more you've got to play with in terms of varying the ratio between wheel torque and rpm via GEARING. Power to weight ratio is king for a good reason.

[Seattlecarnut]

How the hell was David able to make videos? I thought his videos were removed from You Tube?

[chughes374]

@Seattlecarnut Because he's awesome. His old videos were re-uploaded by third parties. chughes376 and davidsfarmfans. His new channel is davidsfarmlives (with new videos)

[Seattlecarnut]

@chughes374 I'll have to check them out. Thanks.

[ngreatshark]

I've been trying to understand the relationship between torque & horsepower for years, and in just the few minutes it took to watch this video, the light finally came on for me. Thanks so much!

[techman360]

Thank you so much for explaining!!! For those of you who might not have caught it, torque is how much 'force' or 'power' the engine is creating, and HP is the amount of work it can do in relation to the RPM's. He explaines it so well at 4:08 - 5:03.

[Dillon1791]

I had no idea it was going to be David! ::Faints::

[chughes374]

@Dillon1791 his new channel is 'davidsfarmlives' . My channel is just a re-uplaoad

[Dillon1791]

@chughes374 i knew about his new channel for a while-i still had no idea it would be him here tho. 

[Jah2070]

Alot of knowledge gained from this video, thanks alot for the information.

[hattrickzero]

Ok, but what is torque and what is horsepower?

[vT4K]

thanks man sweet video

[levin666]

torque: how much work can be done

hp: how much work is done in a certain time.

[BAMBAM3316]

I still haven't heard an understandable explanation for horsepower yet. Or I keep missing the explanation. 

[thecelebspy]

Very helpful thanks!,

[ammarns]

I was able to understand the meaning of torque, but i'm still confused about what the horse power of the engine really is :(

[alow070]

@ammarns Hp is how fast something is moved. 1 Hp = 75 Kg moved up 1 meter in 1 second. Hp is also nothing that can be measured but it's calculated. You can measure both torque (engine force) and rpm (engine speed) and use these to calculate the Hp.

[rubypuppy7]

thanks Dave glad ur on you tube some where

[12edDemon]

needs more views

[offroadskillz]

yeah that was very helpful

[proto993]

thanks! very usable information

[neumei626]

Masterfully done!

[ahmadbila06]

very nicely explained... i love it!